如何防止 geom_segment 中的重叠段

Question

我正在尝试使用geom_segment 将不同的范围（线）映射到图中的不同区域（见下文），但某些范围重叠并且根本无法显示。 这是数据框的一个最小示例：

start = c(1, 5,8, 14)
end =c(3, 6,12, 16)
regions = c(1,2,3, 4)

regions = data_frame(regions, start, end)

from = c(1,2, 5.5, 13.5)
to = c(3,2.5,6, 15)

lines = data_frame(from, to)

我用geom_rect 绘制区域，然后用geom_segment 绘制范围（线）。 剧情是这样的：

plot_splice <- ggplot() +
  scale_x_continuous(breaks = seq(1,16)) +
  scale_y_continuous() +
  geom_hline(yintercept = 1.6,
             size = 20,
             alpha = 0.1) +
  geom_rect(
    data = regions,
    mapping = aes(
      xmin = start,
      xmax = end,
      ymin = 1.5,
      ymax = 1.8,
    )) +
  geom_segment(
    data = lines,
    x = (lines$from),
    xend = (lines$to),
    y = 1.48,
    yend = 1.48,
    colour = "red",
    size = 3
    ) +
  ylim(1.0, 2.2) + 
  xlab("") +
  theme_minimal() 

第一个图是使用代码生成的图，而第二个图是所需的图。

如您所见，第二行与第一行重叠，因此您根本看不到第二行。

如何更改代码以生成第二个图？

我正在尝试使用 ifelse 语句，但不确定 test 参数应该是什么： 我希望它检查每个范围（线）是否与任何先前的范围（线）重叠以将y 位置更改为.05 左右，因此它不会重叠。

lines <- lines %>% 
  dplyr::arrange(desc(from))

new_y$lines = ifelse(from[1] < to[0], 1.48, 1.3)

geom_segment(
    data = lines,
    x = (lines$from),
    xend = (lines$to),
    y = new_y,
    yend = new_y,
    colour = "red",
    size = 3
    )

Answer 1

您的geom_segment 调用未使用任何美学映射，这是您通常如何让 ggplot 元素根据特定变量（或一组变量）更改位置的方式。

最好在调用 ggplot 之前根据重叠区域的数量计算 geom_segment 的堆叠。这允许您将 x 和 y 值传递到美学映射中：

# First ensure that the data feame is ordered by the start time
lines <- lines[order(lines$from),]

# Now iterate through each row, calculating how many previous rows have
# earlier starts but haven't yet finished when the current row starts.
# Multiply this number by a small negative offset and add the 1.48 baseline value
lines$offset <- 1.48 - 0.03 * sapply(seq(nrow(lines)), function(i) {
   with(lines[seq(i),], length(which(from < from[i] & to > from[i])))
   })

现在做同样的情节，但在geom_segment内部使用美学映射：

 ggplot() +
  scale_x_continuous(breaks = seq(1,16), name = "") +
  scale_y_continuous(limits = c(1, 2.2), name = "") +
  geom_hline(yintercept = 1.6,
             size = 20,
             alpha = 0.1) +
  geom_rect(
    data = regions,
    mapping = aes(
      xmin = start,
      xmax = end,
      ymin = 1.5,
      ymax = 1.8,
    )) +
  geom_segment(
    data = lines,
    mapping = aes(
      x = from, 
      xend = to, 
      y = offset, 
      yend = offset),
    colour = "red",
    size = 3
    ) +
  theme_minimal()